1. Field of the Invention
This invention generally relates to a color liquid crystal display, and more particularly, to a transmissive or transflective color liquid crystal display.
2. Description of the Related Art
In general, a transmissive color liquid crystal display (LCD) is provided with white light sources to illuminate the liquid crystal cell thereof. After passing through the inner color filters of the liquid crystal cell, the illuminating white light is filtered into three primary colors of red, green and blue. The mixture of the three primary colors can produce a full-color display image. The cold cathode fluorescent lamps (CCFLs) or white LEDs are commonly used to generate the illuminating white light.
With reference to FIG. 1, a conventional color LCD 100 includes a liquid crystal cell 140 comprising a liquid crystal layer 146 sandwiched in between two transparent substrates 142 and 144. A plurality of color filters 148 is disposed between the substrates 142 and 144. Polarizers 150 and 130 are arranged such that the substrates 142 and 144 are between the polarizers 150 and 130. A backlight module 110 including a white light source 112 such as white LED is disposed below the polarizer 130.
After passing through the polarizer 130, the white light emitted from the white light source 112 is polarized into a light of specified polarization and then incident upon the liquid crystal cell 140. When the polarized white light passes through the color filters 148 and travels through the twisted liquid crystal molecules, the polarized white light is filtered and transformed into red, green and blue lights of different polarization. The filtered lights are then incident upon the polarizer 150 and turned into lights of different colors and intensities. The mixture of the lights of different colors and intensities produces a full-color display image.
In order to emit the illuminating white light, a fluorescent material is coated on the surface of the LED 112 or doped in the LED 112. The fluorescent material can convert the blue light emitted from LED to the illuminating white light. Because the composition of the fluorescent material can substantially change the rate of the blue light converted to the yellow light, it is difficult to achieve the desired composition of the fluorescent material. Furthermore, it is still unsatisfied for the color purity and brightness of the color lights which are converted from the white light after it passes through the color filters.
In view of the above, there exists a need to provide a color liquid crystal display that has improved color purity and brightness.